Dubai's Emirates said it had suspended flights to Guinea over Ebola, becoming the first major international airline to impose a ban in response to the outbreak of the deadly virus in West Africa.

Flights would be suspended until further notice, the airline said in a statement on its website.

''The safety of our passengers and crew is of the highest priority and will not be compromised,'' it said.

The Ebola outbreak, which began in Guinea and has spread to Liberia and Sierra Leone, has killed more than 700, making it the deadliest since the virus was discovered almost 40 years ago.

Sierra Leone declared a state of emergency on Wednesday.

In line with guidelines from International airlines association IATA and the World Health Organisation, several major airlines and international airports have started health screening of passengers on flights from West Africa.

But IATA said on Thursday the WHO was not recommending travel restrictions or border closures, and there would be a low risk to other passengers if an infected person flew.

Nigeria's largest airline Arik Air, which flies to a limited number of international destinations including London, has stopped flights to Liberia and Sierra Leone.

Pan-African airline Asky was suspended by Nigeria's civil aviation authorities for bringing the first Ebola case to the country's largest city Lagos.

West African leaders agreed on Friday to take stronger measures to try to bring Ebola under control and prevent it spreading outside the region

.Emirates, which does not fly to either Liberia or Sierra Leone, said any further actions in connection with the outbreak would be ''guided by the advice and updates from the government and international health authorities.''

"Over the last weeks, there has been a significant surge in the epidemic - the number of cases has increased dramatically in Sierra Leone and Liberia, and the disease has spread to many more villages and towns," Doctors Without Borders said in a statement.

"After a lull in new cases in Guinea, there has been a resurgence in infections and deaths in the past week."

At least 729 people have died since cases first emerged in March: 339 in Guinea, 233 in Sierra Leone, 156 in Liberia and one in Nigeria.

Two American health workers in Liberia have been infected, and an American man of Liberian descent died in Nigeria from the disease, health authorities there say.

Plans were underway to take the two American aid workers - Nancy Writebol and Dr. Kent Brantly - back to the US.

A small private jet based in Atlanta has been dispatched to Liberia. Officials said the jet was outfitted with a special, portable tent designed for transporting patients with highly infectious diseases.

While health officials say the virus is transmitted only through direct contact with bodily fluids, many sick patients have refused to go to isolation centres and have infected family members and other caregivers.

The fatality rate has been about 60 perbcent, and the scenes of patients bleeding from the eyes, mouth and ears has led many relatives to keep their sick family members at home instead. Sierra Leone is now sending teams door-to-door in search of Ebola patients and others who have been exposed to the disease.

Chan emphasized Friday that the general public "is not at high risk of infection," but also said the Ebola virus should not be allowed to circulate widely.

"Constant mutation and adaptation are the survival mechanisms of viruses and other microbes," she said.

"We must not give this virus opportunities to deliver more surprises."

Randy Schoepp, chief of diagnostics at the US Army Medical Research Institute of Infectious Diseases, which is running the only lab in Liberia testing Ebola samples, said: "The virus is getting to large, dense, city areas. We're now getting samples (to test) from all over."

But he said "we're only seeing a small portion of the cases out there," partly because many drivers are scared to transport vials of blood that may contain Ebola to the lab.